The conventional technique described in Patent Literature 1 below discloses a power-factor improving circuit that improves the source power factor to reduce harmonic components contained in the input current and that selects a full-wave rectification mode or a double-voltage rectification mode and controls the short-circuit start time and short-circuit time of a short-circuit element by open-loop control so as to realize the functions to improve the power factor and to boost the voltage. That is, according to the conventional technique by Patent Literature 1, a rectifying circuit is controlled to go into the full-wave rectification mode or the double-voltage rectification mode by turning on and off a switch for switching the rectifying circuit, and therefore the direct-current output voltage range of the power-factor improving circuit is divided broadly into two levels; and the divided area of each of the two levels is further divided by open-loop variable short control of the short-circuit element into two levels, one without an improved power factor and one with an improved power factor, for a total of four levels of direct-current output voltage areas; so that the power factor on the high-load side can be improved with the output range of the direct-current output voltage being extended.
According to the conventional technique described in Patent Literature 2 below, provided is a direct-current voltage control unit that outputs a direct-current voltage control signal corresponding to the deviation value between a direct-current output voltage reference value set corresponding to the load and the voltage across the terminals of a smoothing capacitor; and also provided is a current reference arithmetic unit that outputs a current reference signal on the basis of the product of the control signal from the direct-current voltage control unit and a sinusoidal synchronizing signal synchronous with an alternating-current power supply. By comparing this current reference signal and the current on the alternating-current side of a rectifying element, a switch element is on/off-controlled at a high frequency, and thereby the direct-current output voltage is controlled to be at a desired value while the alternating-current input current is controlled to be sinusoidal. Therefore the occurrence of harmonics can be suppressed with the source power factor being at one.